"Popped knees" is a complex collection of different injuries to bone and/or soft tissue structures within the knee joint of one or both forelimbs. Even though a bony fracture is much different from a soft tissue injury in terms of ultimate treatment, distinguishing these different types of injury is usually impossible without technical support such as x-ray, ultrasound, and possibly even arthoscopic exploration surgery. Therefore, from the horse owner's point of view, all severe injuries to the knee joint are lumped together and handled as though they were a worst-case scenario until a detailed veterinary examination can prove otherwise. The important thing from the emergency treatment point of view is recognizing that the knee joint is the focus of the horse's problem.
What you see from the outside The horse will "walk wide," swinging the leg to the outside to move it forward without bending the sore knee. The involved joint might be puffy (called "hygroma") and warm, depending on the severity and freshness of the injury and depending on whether it involves bone or soft tissue or both. In most cases, the problem is obvious when the foot is picked up and the joint is forced to flex—the horse will flinch or otherwise display a painful response. In the normal horse, you should be able to bend the leg to easily touch the heel to the elbow. The horse with a sore knee will tense the leg and prevent the flexion if it hurts, and the lameness will be exaggerated temporarily when you put the foot back down. Other signs: the horse might resent having the joint manipulated, and the joint might be tender to the touch.
What causes knee injuries?
There are three main types of sudden, severe knee lameness common in performance horses:
- bone fractures
- ligament strains
- inflammation of the joint capsule
Fatigue plays a major role in knee injuries, and some activities predispose to each type of injury.
The most dramatic knee joint injury involves chip and/or crushing fractures of one or more bones inside the carpal joint. With fatigue, the muscle allow the carpal bones to move out of proper alignment when the joint is stressed, and since they're supposed to intelock perfectly during maximum load, fractures are highly likely when they're out of position and 1,100 pounds of mass are barreling down the leg at high speed. The most common victims are youngsters in training, especially heavy-bodied, fast-sprinting Quarter Horses that can pour on the speed early in their careers, without prior conditioning. Youngstres in jump training are at risk particularly when asked to jump before they've developed adequate strength in their legs. Carpal chip fractures are frequent findings in horses that run downhill, an activity that is common during endurance races, delivering a concussive beating to the knees. Weekend warriors' horses are at risk because of lack of conditioning and marshmallow-soft muscles that are unable to absorb much of the stress of load-bearing.
One of the most common soft tissue injuries in the knee is inflammation of the ligaments that hold the rows of carpal bones in position. This is most often seen in youngsters in early training and is a result of stress on the knee joints from a training program that is too strenous too soon. Rather than concussive insults, it's quick changes in direction, jack-rabbit starts, sliding stops, and extended trots that are most often implicated&mdahs;any moves that tend to twist, or bend the little cube-shaped bones out of their neat, orderly rows, or that ask the hinge-like joint to overextend (common in youthful, poorly executed trots) or bend sideways (common in young cutting horses.)
The other common non-bony carpal joint injury is inflammation of the joint capsule, also known as synovitis/capsulitis. It is the result of excessive stress on the joint under load, particularly when the ligaments are loose.
Emergency care
- CONFINE Strict stall confinement for 48 hours is a must to further limit damaging forces to the injured leg. As soon as it's safe to do so (the leg is well protected and the quickest route has been mapped out), the horse should be transported to a competent equine orthopedist for a specific diagnosis.
- ICE Ice the knee, using crushed ice packs, bags of frozen peas, chemical cold packs, or cold water rinses. Ice on: 5 minutes. Ice off: 15 minutes. repeat cycle for 48 hours.
- IMMOBILIZE Apply a Class III or Class IV knee bandage to limit movement and minimize swelling. Until the exact nature of the injury is known, it's critical that further damage to the inside of the joint be prevented by immobilizing the leg. Shredded ligaments, torn cartilages, and shrp bone fragments can combine to make the problem much worse if the horse is permitted to move the leg freely.
- GIVE AN ANTIINFLAMMATORY An intramuscular injection of an antiinfalmmatory medication can keep inflammation and its byproducts from worsening the damage, and its pain-killing action will help to make the horse more comfortable. Do not give the medication if for some reason you can't properly bandage the leg—if you relieve the pain without restricting leg movement, you set the stage for massive additional damage.
References: Emergency! by Karen Hayes, D.V.M.